I loved the characters of Tom Perrotta’s new novel, “Mrs. Fletcher,” but I was worried about them. After all, they’re in a social satire by the author of “The Leftovers,” “Little Children” and “Election,” and they’re making mistakes and misbehaving right and left — surely they’d have to pay. So convinced was I that comeuppance was at hand that the surprise happy ending almost brought me to tears. Perrotta has been called the “Steinbeck of suburbia” and an “American Chekhov,” but with “Mrs. Fletcher,” he’s become the Jane Austen of 21st century sexual mores.

Mrs. Fletcher — Eve — is a 46-year-old divorcee who, as the story opens, is about to take her only son to college. Brendan is a handsome, athletic, garden-variety lout who cannot be bothered to help his mother load the van but does deign to receive a last-minute sexual favor from the high school girlfriend he just dumped. Eve overhears her son address the young woman in such crude language that, much as she would like to avoid it, she has to say something.

“She didn’t want him to begin college without understanding that there was a fundamental difference between sexual relationships in real life and the soulless encounters he presumably watched on the internet,” Perrotta writes.

But once they get in the van, Brendan plugs in his headphones and pretends to sleep, so Eve avoids the discussion after all. Off he goes into the complicated sexual landscape of the modern college campus, clueless as ever. Perrotta cannily has Brendan narrate his parts of the story, making it impossible to simply write him off as a stereotypical jackass bro — though Lord knows he deserves it.

In an end-run around the loneliness of her empty nest, Eve signs up for a community college course called “Gender and Society: A Critical Perspective,” taught by an transgender woman named Margo Fairchild. This class will do a lot more for Eve than bring her up to speed on “the persistence of sexism in a ‘postfeminist’ culture, and the subversion of heteronormative discourse by LGBTQIA voices.”

Speaking of soulless encounters on the internet: Lonely Eve has also developed a nightly porn habit. Quickly she goes from being a naif who barely knows what a cougar is to someone with, well, nonheteronormative tastes. Meanwhile, in the real world, she finds herself attracted to both a younger woman who works for her at the local senior center, and an 18-year-old boy in her class at school; no one is more shocked than she is when these fantasies cross over into reality.

Because he has perfect pitch when it comes to shading the emotional states of his characters, Perrotta can make you believe anything — whether it’s an outlandish porn scenario come to life or a simple exchange between mother and son. When Brendan is home from college on Valentine’s Day, Eve lovingly prepares a meal — then learns he has other plans. “Why can’t you eat here and then go out?” she suggests.

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“ ‘We’re gonna get pizza and watch the hockey game. Is that a problem?’

“ ‘Fine. Do what you want.’

“ ‘Jeez, what’s the big deal?’ he asked. ‘When I was away at school, you ate by yourself every night.’ ”

Brendan’s casual cruelty, Eve’s martyrish reaction, and then her attempt to get through the rest of her depressing, solitary evening feel almost documentary in their realism (take it from a vet). Scene by scene, Perrotta builds that capital into a delicious, tragicomic and finally forgiving take on the mistakes we modern people can’t seem to stop making. “Mrs. Fletcher” is a delight.